Abstract: An improved algorithm, which is called MW_Apriori algorithm is proposed based on the matrix and weight in this paper.Firstly, build the 0-1transaction matrix by scanning transaction database.Then items and transactions are assigned to weights, and the weighted support of items are caculated, accordingly gettig the frequent itemsets.Experiments show that MW_Apriori algorithm avoids rescanning the database, making the cost of time and space significantly reduced, at the same time can effectively mine the hidden and valuable rare events.